John and Sherlock were together pre-Afghanistan, and a younger!Sherlock had almost a twink-like look about him. He was a little thinner, less muscular, and all around more feminine looking - in fact, one of their favorite role-plays was him as a woman (cross-dressing welcome too, but not required).
However, while John was away, Sherlock stopped sending him updated pictures. Because he was getting older and more mature-looking, he was losing that twink-like appearance and was afraid John wouldn't want him anymore. John, completely oblivious, is none-the-wiser to Sherlock's distress.
John returns home to find a stranger in their flat, which is actually Sherlock. Cue Sherlock anxiously trying to keep up the charade by any means necessary... and it all coming out in the wash.
Bonus:
If anon choses the cross-dressing route...
+100000 if Sherlock attempts to fit into one of the outfits, only to be dismayed when it rips because he's taller/muscles have gotten larger/etc.
Johnlock, Pre-Afghanistan Relationship
However, while John was away, Sherlock stopped sending him updated pictures. Because he was getting older and more mature-looking, he was losing that twink-like appearance and was afraid John wouldn't want him anymore. John, completely oblivious, is none-the-wiser to Sherlock's distress.
John returns home to find a stranger in their flat, which is actually Sherlock. Cue Sherlock anxiously trying to keep up the charade by any means necessary... and it all coming out in the wash.
Bonus:
If anon choses the cross-dressing route...
+100000 if Sherlock attempts to fit into one of the outfits, only to be dismayed when it rips because he's taller/muscles have gotten larger/etc.